A multi-way valve of this type is disclosed in German patent application No. 44 41 150, for example. The slide of this multi-way valve is displaced in an axial direction by way of an axially movable and electromagnetically adjustable tappet. When the ABS control detects a locking wheel, for example, this will activate an electromagnetic control device, i.e., current flows through a coil and causes displacement of an armature connected to the tappet so that the slide separates the high-pressure source from the wheel brake in terms of flow and, subsequently, the tappet opens a seat valve interposed between the wheel brake and the low-pressure accumulator.
Although the operation of the prior art multi-way valve is satisfactory, the valve is destined for use in a defined vehicle class with a determined braking pressure range. The size or the power of the electromagnetic drive which is necessary to actuate a seat valve is determined by the valve opening cross-section which, in turn, is dictated by the braking pressure range for different vehicles. The result is that a great number of differently dimensioned seat valves must be manufactured and kept at hand.
Generic European patent application No. 0 369 412 discloses an electromagnetically actuatable multi-way control valve for slip-controlled hydraulic automotive vehicle brake systems which includes a slide in a housing member whose first control edge that is effective as a variable orifice normally has a pressure fluid connection between a port of the high-pressure source and the port of a wheel brake which opens into the housing member remote from the slide. To this end, a central bore provided with an invariable orifice is arranged in the slide. The slide is configured as a flow control valve permitting adjustment of a constant pressure fluid flow between the high-pressure source and the wheel brake irrespective of the electromagnetic energization of a valve coil by the hydraulic control position of the slide. When the valve coil is energized electromagnetically, the slide is urged to adopt a position where the first control edge isolates the port of the high-pressure source from the port of the wheel brake, while second control edge on the slide opens a throttled connection between the port of the wheel brake and a port of a low-pressure accumulator by way of the central bore in the slide.
An object of the present invention is to provide a multi-way control valve of the type mentioned hereinabove which has very small overall dimensions and can be used on a great number of vehicle classes, that means when various braking pressure conditions prevail.
In a multi-way valve of the type mentioned hereinabove, this object is achieved by the present invention because a valve member which closes the valve between the wheel brake and the low-pressure accumulator is provided by the slide, and in the closed condition of this valve both front surfaces of the slide are acted upon by hydraulic medium to which the pressure prevailing on the wheel brake is applied and which may escape to the low-pressure accumulator when the seat valve is opened.
This achieves a pressure balance on both sides of the valve member according to the present invention so that the electromagnetic drive can be correspondingly reduced in dimensions. Also, the present invention renders it possible to use one single type of multi-way valve on various vehicle classes.
Favorably, the valve between the wheel brake and the low-pressure accumulator is a seat valve so that the slide is adapted to be urged against a sealing seat in order to achieve a pressure-tight separation between the wheel brake and the low-pressure accumulator, on the one hand, and a large and quickly attainable valve opening cross-section, on the other hand.
In a particularly preferred aspect of the present invention, the slide has a second control edge which, together with a corresponding second control edge on the housing member, provides a second variable throttle cross-section in the hydraulic connection between the wheel brake and the low-pressure accumulator. This renders it possible to maintain and adjust the pressure which is applied to the wheel brake during a pressure-maintaining phase.
It is preferred that the first and second control edges of the slide and the housing member are preferably so arranged that upon displacement of the slide in the direction of reducing the pressure on the wheel brake, initially, the first flow cross-section is closed before the second flow cross-section is opened. This permits passing through a pressure control phase where the pressure on the wheel brake can be increased or reduced by displacing the slide to a comparatively small degree.
In a particularly favorable fashion, the flow cross-sections limited by the control edge increase progressively when the slide movement is steady. The result is a very quick response to a change in position of the slide during a pressure control phase.
Further, it is proposed to configure the second control edge of the slide on the front surface of the slide facing the sealing seat so that the slide can be urged against the sealing seat with this second control edge. This ensures a reliable sealing towards the low-pressure accumulator during the normal braking operation, and the second control edge can open the flow cross-section immediately after its lifting from the sealing seat or form a slot-type seal in conjunction with the second control edge of the housing member. The second throttle cross-section can be opened by passing the second control edge.
The above-mentioned measures render it possible by way of the multi-way valve of the present invention to variably adjust a flow cross-section which permits quick initial braking, on the one hand, and a sensitively controlled volume dosing during anti-lock control operations, on the other hand. This is not done, as frequently occurs in prior art ABS multi-way valves, by a differently long maximum opening of the valve (pulse width modulation) but by a combination of pulse width modulation and pulse amplitude modulation (differently large valve openings). This could per se be effected by a force adjustment, that means, by appropriately dimensioning the electromagnetic control device in relation to the resilient counterforce which acts upon the valve member of a seat valve. However, a valve which can be used on several vehicle classes is favorably achieved by the design of the multi-way valve according to the present invention wherein a position control circuit for the valve slide is additionally provided. The slide position of the sensor can then be determined in an advantageous manner by way of an electronic sensor device and is controllable by way of an electronic control device. This permits eliminating disturbing friction forces by the control, and the switching condition of the multi-way valve, that means the position of the slide, is known at any time. This renders it possible, in turn, to exactly predefine the speed of the variation of the opening cross-section. As it was found out that the variation of the pressure gradient is a major source of noises in multi-way valves of this type, the speed of the variation can be reduced to such an extent that the response times are still satisfactory and the noise which occurs during operation is still not disturbing. This is assisted by the above-mentioned progressive course of the opening cross-section which is achieved because the circular supply bore describes the opening surface. This type of regulation or control also eliminates the abutment noise of the armature which is produced during pulse width modulation. When the slide is moved in the direction of its first end position after deactivation of the ABS control, a preferably elastomeric sealing seat achieves a major damping effect when the slide is moved to bear against it.